1. Field of the Invention
The invention relates to a ceramic capacitor having a one-layer structure or a laminated structure in which one or more than one dielectric ceramic layer is (are) sandwiched between two or more internal electrodes, and a method for fabricating the same.
2. Description Of Related Art
In a conventional method for fabricating a laminated ceramic capacitor, a desired pattern of conductive paste consisting mainly of noble metal such as platinum or palladium is printed on a non-sintered ceramic sheet (a green sheet) consisting essentially of dielectric ceramic material powder. Then, a plural number of the green sheets are laminated, pressed and attached to each other, and the laminated green sheets are fired at a temperature in the range of 1300.degree. C. to 1600.degree. C. under an oxidative atmosphere. The non-sintered ceramic sheets become dielectric ceramic layers by the firing and the conductive paste becomes an internal electrode by the firing.
As described above, by adopting the conductive paste consisting mainly of noble metal such as platinum or palladium, a desired conductive internal electrode can be obtained without oxidation thereof even if the material thereof is fired at a high temperature in the range of 1300.degree. C. to 1600.degree. C. under an oxidative atmosphere.
However, noble metals such as platinum or palladium are expensive, so that the laminated ceramic capacitor become very costly.
In order to resolve the problem described above, the applicants of the present invention have proposed several solutions in Japanese Patent Publication No. 20851/85, Japanese Patent Provisional Publication No. 147404/86, Japanese Patent Provisional Publication No. 147405/86, and Japanese Patent Provisional Publication No. 147406/86.
Japanese Patent Publication No. 20851/85 discloses dielectric ceramic compositions including basic components consisting essentially of EQU {(Ba.sub.x Ca.sub.y Sr.sub.z)O}.sub.k (Ti.sub.n Zr.sub.1-n)O.sub.2
and additional components consisting essentially of Li.sub.2 O, SiO.sub.2 and MO (MO is one or more than one kind of oxide selected from the group consisting of BaO, CaO and SrO).
Japanese Patent Provisional Publication No. 147404/86 discloses dielectric ceramic compositions including basic components consisting essentially of EQU {(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)}.sub.k (Ti.sub.1-z Zr.sub.z)O.sub.2
and additional components consisting essentially of B.sub.2 O.sub.3, SiO.sub.2 and Li.sub.2 O.
Japanese Patent Provisional Publication No. 147405/86 discloses dielectric ceramic compositions including basic components consisting essentially of EQU {(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O}.sub.k (Ti.sub.1-z Zr.sub.z)O.sub.2
and additional components consisting essentially of B.sub.2 O.sub.3 and SiO.sub.2.
Japanese Patent Provisional Publication No. 147406/86 discloses dielectric ceramic compositions including basic components consisting essentially of EQU {(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O}.sub.k (Ti.sub.1-z Zr.sub.z)O.sub.2
and additional components consisting essentially of B.sub.2 O.sub.3, SiO.sub.2 and MO (MO is one or more than one kind of oxide selected from the group consisting essentially of BaO, CaO and SrO).
The dielectric ceramic compositions disclosed in these Publications have a dielectric constant .epsilon..sub.s of at least 5000, and a resistivity .rho. of at least 1.times.10.sup.6 M.OMEGA..multidot.cm. By using one of the above dielectric ceramic compositions as a dielectric layer and a conductive paste consisting mainly of base metal such as nickel (Ni) as internal electrodes and firing same at a temperature of up to 1200.degree. C. under a reductive (non-oxidative atmosphere), ceramic capacitors with improved electric characteristics can be obtained at a low cost.
Recently, electric circuits have become highly dense. These circuits require miniaturization of ceramic capacitors, especially those having a laminated structure. It has been desired to make the dielectric constant .epsilon..sub.s of the dielectric ceramic compositions still larger, without degrading the other electric characteristics below those of the dielectric ceramic compositions disclosed in the above cited references.